For frequencies higher than 10 Hz, the background hazard estimates with and without point source correction were typically similar; the effect of point source correction was primarily observed for lower frequencies. For frequencies higher than 1 Hz, the background hazards estimated typically matched well the PSHA results, notwithstanding the difference in some source parameter randomization details between the CEUS SSC and the NGA-East implementation in the NGA-East GMM report [6]. Figure 4-3 shows an example comparison for the Topeka site. For 1 Hz and lower frequencies, point source correction improved the mean hazard estimate but did not fully correct for the difference in slope, which was consistently lower for the estimated mean hazard than the PSHA result (Figure 4-4). A low frequency adjustment procedure described in Section 4.3 was developed to mitigate this limitation. Low Frequency Adjustment The discrepancy in the estimated low-frequency background hazard curve slope shown in Figure 4-4, was attributed to the following reasons:

For frequencies higher than 10 Hz, the background hazard estimates with and without point source correction were typically similar; the effect of point source correction was primarily observed for lower frequencies. For frequencies higher than 1 Hz, the background hazards estimated typically matched well the PSHA results, notwithstanding the difference in some source parameter randomization details between the CEUS SSC and the NGA-East implementation in the NGA-East GMM report [6]. Figure 4-3 shows an example comparison for the Topeka site. For 1 Hz and lower frequencies, point source correction improved the mean hazard estimate but did not fully correct for the difference in slope, which was consistently lower for the estimated mean hazard than the PSHA result (Figure 4-4). A low frequency adjustment procedure described in Section 4.3 was developed to mitigate this limitation. Low Frequency Adjustment The discrepancy in the estimated low-frequency background hazard curve slope shown in Figure 4-4, was attributed to the following reasons: